In a communication system, energy saving technique directly affects the network lifetime and is gaining importance according to the ubiquitous communication environment, multimedia service environment, and the trend of recent technology such as the small hand-hold wireless devices.
Typical examples of the currently proposed energy saving techniques are technique of powering off the transceiver (e.g. RF module) when no data to transmit or receive exists and technique of allocating minimum power (e.g. adaptive modulation and coding) under constraint conditions (e.g. error rate, transmission rate, transmission delay).
In the former technique, energy is saved by periodically generating or controlling the sleeping period during which the power is saved by turning off the transceiver and the active period during which transmission and/or reception for wireless communication is performed.
In the latter technique, the transmission efficiency may be increased through the adaptation to the channel state. Particularly, the opportunistic scheduling technique, a scheduling technique obtained by extending the latter technique to the multiuser environment may increase the transmission efficiency according to the benefit of the multiuser diversity. However, the opportunistic scheduling technique requires the channel state information feedback from all users. This causes additional consumptions of energy and wireless resources for the information feedback. Particularly, more information feedbacks are required in the MIMO environment or multi-carrier (e.g. OFDM) environment so that the additional consumptions are increased. In order to overcome the above drawback, a partial information feedback technique (i.e. reporting only the information regarding the partial sub-channel having an excellent channel state or reporting only if the channel state is excellent) is proposed. The partial information feedback technique focuses on minimizing the additional consumption of the wireless resources by minimizing the information amount of the feedback. However, the partial information feedback rarely considers the energy consumption. To report the channel state information, energy is consumed by the operation of obtaining the channel state information (e.g. operation of receiving pilot signals, preambles, etc. and estimating channel quality based on the received signal) and the operation of transmitting the channel state information. Particularly, in conventional techniques, the energy consumption for the former operation is not considered at all.
As a result, a scheduling technique for a wireless cellular network improved in energy efficiency is required and, more preferably, a scheduling technique, which provides the opportunity to all users in a fair manner, is required.